The use of flowlines to simplify routing complexity in two-stage flowshops

Flexible manufacturing systems are often designed as flowshops supported by automated material handling devices that facilitate routing among any two processors of adjacent stages. This routing structure is complex, and results in excessive capital investment and costs of management. In this paper we propose a decomposition of two-stage flowshops into smaller independent flowlines that allow for unidirectional routing only. We solve optimally the problem of minimizing makespan on two parallel flowlines, by means of a Dynamic Programming algorithm (DP). Based on DP we develop lower bounds on the throughput performance of environments that consist of more than two flowlines. We present several heuristic algorithms and report their optimality gaps. Using these algorithms, we show that the decomposition of two stage flowshops with complicated routing into flowline-like designs with unidirectional routing is associated with minor losses in throughput performance, and hence significant savings in material handling costs.